Method and apparatus for disinfecting a product by surface treatment thereof

ABSTRACT

A method and an apparatus in form of a disinfecting apparatus comprising a steam device for combatting germs on the surface of products, in particular of food products. The apparatus employs a combination of steam and ultrasound to kill germs on the surface of a product which is conveyed past the steam device. Pressurized steam is fed through a steam passage to an opening conveying the steam to a cavity, in which the steam is made to oscillate at a ultrasonic frequency. The oscillations in the steam prevent the steam from heating the products excessively, while germs presents on the surface of the products are heated and killed.

TECHNICAL FIELD

[0001] The invention relates to a method for disinfecting a product bysurface treatment thereof, steam of a liquid, preferably aqueous steam,and sound, preferably ultrasound, being discharged to the surface of theproduct.

[0002] When processing and subsequent packing food products it isdesirable to kill germs, such as spores, micro-organisms and the likepresent on the surface of the food products and on other firm surfaces.It is known to heat-treat food to kill germs. However such a heattreatment usually causes unwanted changes in the flavour and texture ofthe treated food and may at worst spoil the food. It is also known toremove impurities from the surface of a product by ultrasonic treatmentthereof.

BACKGROUND ART

[0003] Japanese published specification No JP-0714 3999A discloses asterilization apparatus, in which the instruments to be sterilized firstare exposed to ultrasound and then autoclaved by means of high-pressuresteam, and finally irradiated with ultraviolet light. This principle is,however, not suitable for the treatment of food inter alia due to thehigh temperatures used during the autoclave process.

[0004] Furthermore EP 0711566A1 discloses a method and an apparatus fordegerminating dental instruments. The apparatus employs variousprinciples for combatting germs, eg. treatment with jets of steam, hotair, ultrasound bath, electromagnetic radiation, etc. This apparatus is,however, not suitable for the treatment of food, as too high heatvolumes are absorbed by the treated products in many of the proposedmethods.

[0005] It is moreover known to heat the surface of for instances foodproducts by means of steam to kill germs. However, in order to obtainthe desired kill effect the outermost layers of the treated food aredamaged as a result of excessive exposure.

[0006] It is further known from Russian patent No. 2000058 to sterilisefluid food products by means of a combination of steam and ultrasound.The food is fed to a container and a layer of the fluid food is formedby centrifugal force. Steam is supplied to the food from the innersurface of the container. The steam is injected through a plurality ofnozzles, whereby ultrasonic oscillations are generated in the fluidfood. During condensation of the steam a cavitation is formed. The useof this treatment method is limited for a number of reasons:—it is onlysuitable for fluid food products, —a centrifuge is required, and—wateris supplied to the food due to the condensation of aqueous steam. Thistype of condensation is preferably avoided.

DESCRIPTION OF THE INVENTION

[0007] The object of the invention is to provide a method for thedisinfection of a product and which is suitable for effectively killinggerms on the surface of the product without inducing too much heat tothe product.

[0008] A method of the above type is according to the inventioncharacterised in that ultrasound is generated at the same time as thesteam is discharged and made to oscillate at a frequency in theultrasonic range at such a high acoustic pressure that the migration ofthe individual molecules exceeds the dimension of the bacteria or germsto be killed.

[0009] The ultrasound in the steam thus generates such high particleoscillations and particle velocities that the water molecules arealternately pumped to and fro the surfaces of the products. As a result:

[0010] 1. Power is supplied in form of steam;

[0011] 2. The steam zone around the product is continuously removed toprevent condensation and insulation;

[0012] The ultrasound in the steam thus generates such high particleoscillations and particle velocities that the water molecules arealternately pumped to and from the surfaces of the products. As aresult:

[0013] 1. Power is supplied in form of steam;

[0014] 2. The steam zone around the product is continuously removed toprevent condensation and insulation;

[0015] 3. The natural microstructures in the surface do not preventsteam from reaching all germs.

[0016] This entails that

[0017] 1. The surface of the product is heated to the temperature of thesteam considerably faster than if the heat is conducted through the airzone surrounding the product.

[0018] 2. Germs hidden in natural pockets and spores are heated withouthardly affecting the food per se.

[0019] During treatment the temperature inside the product decreases asa function of the depth. This also applies to germs on the surface. Inbiological products the germs are typically several times smaller thanthe cell size of the product. This means that the germs reach a coretemperature exceeding 70° C. at a time, at which the thermal gradienthas only penetrated a few micrometers into the surface cells of theproduct.

[0020] When the treatment is subsequently completed, the amount ofenergy absorbed by the cells of the product distributes itself andresults in a general heating of the product. Since the volume of thecells of the product exceeds the volume of germs, the total amount ofheat induced during processing is very small and thus harmless to theproducts. The processing time is comparatively short, preferably only afew seconds.

[0021] In a particularly advantageous embodiment of the invention theultrasound is generated by conducting steam through aultrasound-generating device and causing the steam to oscillate at afrequency in the ultrasonic range at such a high acoustic pressure thatthe migration of the individual molecule exceeds the dimension of thebacteria or germs to be killed.

[0022] The ultrasound-generating device may for instance be formed of ajet stream and a cavity.

[0023] The invention further relates to a disinfection apparatus forcarrying out the method comprising a steam device for combatting germson the surface of a solid product, especially of a solid food product,said steam device having at least one steam passage and an opening.

[0024] The disinfection apparatus is characterised in that a cavity isprovided adjacent the opening, which in use is adapted to be suppliedwith a jet of aqueous steam under a comparatively high pressure throughthe steam passage, whereby the aqueous steam diffused from the openingis made to oscillate at a frequency determined by the cavity. As aresult a particularly advantageous disinfection apparatus is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is described in greater detail below with referenceto the accompanying drawings, in which

[0026]FIG. 1 shows the diffusion of a steam jet from a steam device of adisinfection apparatus according to the invention,

[0027]FIG. 2 shows an embodiment of a steam device in form of adisc-shaped disc jet,

[0028]FIG. 3 is a sectional view along the diameter of the steam devicein FIG. 2,

[0029]FIG. 4 shows a steam device shaped as a elongated body,

[0030]FIG. 5 shows a steam device of the same type as in FIG. 4 shapedas a closed curve, and

[0031]FIG. 6 shows a steam device of the same type as in FIG. 4 shapedas an open curve.

BEST MODES FOR CARRYING OUT THE INVENTION

[0032] The disinfection apparatus shown in FIG. 1 for carrying out themethod according to the invention comprises a steam device 1 shaped as adisc-shaped so-called disc jet comprising an outer part 5 and an innerpart 6, which is displayed in a sectional view in the figure.Pressurized water is passed from a steam chamber 10 through a steampassage 3 defined by the outer part 5 and the inner part 6 to an opening2, from which the steam is discharged in a jet towards a cavity 4provided in the inner part 6. The steam may be made from distilled ordemineralized water. If the steam pressure is sufficient highoscillations are generated in the steam fed to the cavity 4 at afrequency defined by the dimensions of the cavity 4. By adapting thedimensions of the cavity 4 for instance such that its acoustic naturalfrequency ranges between 20 kHz and 25 kHz, the steam device 1 generatesacoustic oscillations from the opening 2 provided the steam pressure issufficiently high. A further increase of the steam pressure does notchange the frequency significantly, but the acoustic pressure deliveredby the steam device 1 is heavily increased. A steam device of the typeshown in FIG. 1 is able to generate ultrasonic acoustic pressures of upto 160 dB_(SPL) at a steam pressure of about 4 atmospheres. The steamdevice 1 may be made from brass, aluminium or stainless steel in asuitable stainless material or in any other sufficiently hard material.The material merely has to withstand the acoustic pressure andtemperature to which the steam device is subjected during use. Themethod of operation is also shown in FIG. 1, in which the diffused steam7 is made to oscillate by the cavity 4. The diffused oscillating steamis directed towards a subjacent conveyor 9, whereon the products 8, eg.the food products, to be disinfected, are arranged. The products 8 areconveyed at a predetermined velocity corresponding to the desireddisinfection degree. The emitted oscillating steam may optionally beused to disinfect seeds.

[0033] An optional embodiment of a steam device according to theinvention, ie. a so-called disc jet, is shown in FIG. 2. The steamdevice 1 comprises an annular outer part 5 and a cylindrical inner part6, in which an annular cavity 4 is recessed. Through an annular steampassage 3 steam may be diffused to the annular opening 2 from which itmay be conveyed to the cavity 4. The outer part 5 maybe adjustable inrelation to the inner part 6, eg. by providing a thread or anotheradjusting device (not shown) in the bottom of the outer part 5, whichfurther may comprise fastening means (not shown) for locking the outerpart 5 in relation to the inner part 6, when the desired intervaltherebetween has been obtained. Advantageous dimensions of the steamdevice shown in FIG. 2 may be an external diameter of the outer part 5of for instance 80 mm, an internal diameter of the rim of the opening 2of about 22 mm, a diameter of the tip of the inner part 6, in which thecavity 4 is provided, of about 15 mm, and a cavity 4 having an internaldiameter of about 10 mm and a width ranging from 1.5 to 2 mm. Such asteam device generates a frequency of about 19 kHz at a steam pressureof 4 atmospheres. The molecules of the steam are thus able to migrate upto 36 μm about 19,000 times per second at a maximum velocity of 4.5 m/s.These values are merely included to give an idea of the size andproportions of the steam device and by no means limit of the shownembodiment.

[0034]FIG. 3 is a sectional view of the steam device 1 in FIG. 2 so asto render the shape of the opening 2, the steam passage 3 and the cavity4 more clearly. It is further apparent that the opening 2 is annular.The steam passage 3 and the opening 2 are defined by the substantiallyannular outer part S and the cylindrical inner part 6 arranged therein.The steam jet discharged from the opening 2 hits the substantiallycircumferential cavity 4 formed in the inner part 6, and then exits thesteam device 1. As previously mentioned the outer part 5 defines theexterior of the steam passage 3 and is further bevelled at an angle ofabout 30° along the outer surface of its inner circumference forming theopening of the steam device, wherefrom the steam jet may expand whendiffused. Jointly with a corresponding bevelling of about 60° on theinner surface of the inner circumference, the above bevelling forms anacute-angled circumferential edge defining the opening 2 externally. Theinner part 6 has a bevelling of about 45° in its outer circumferencefacing the opening and internally defining the opening 2. The outer part5 may be adjusted in relation to the inner part 6, whereby the pressureof the steam jet hitting the cavity 4 may be adjusted. The top of theinner part 6, in which the cavity 4 is recessed, is also bevelled at anangle of about 45° to allow the oscillating steam jet to expand at theopening of the steam device.

[0035] As an optional embodiment of the steam device of the disinfectionapparatus an elongated, rail-shaped body 1 is shown in FIG. 4, said bodybeing functionally equivalent with the embodiments shown in FIG. 1 andFIG. 2, respectively. In this embodiment the outer part comprises twoseparate rail-shaped portions 5 a and 5 b, which jointly with therail-shaped inner part 6 form a steam device 1. Two steam passages 3 aand 3 b are provided between the two portions 5 a and 5 b of the outerpart 5 and the inner part 6. Each of said steam passages has an opening2 a, 2 b, respectively, conveying emitted steam from the steam passages3 a and 3 b to two cavities 4 a, 4 b provided in the inner part 6. Oneadvantage of this embodiment is that a rail-shaped body is able to coata far larger surface area than a circular body. Another advantage ofthis embodiment is that the steam device may be made of extrudedaluminium, whereby the cost of materials is reduced.

[0036] The embodiment of the steam device shown in FIG. 4 does not haveto be rectilinear. FIG. 5 shows a rail-shaped body 1 shaped as threecircular, separate rings. The outer ring defines an outermost outer part5 a, the middle ring defines the inner part 6 and the inner ring definesan innermost outer part 5 b. The three parts of the steam device jointlyform a cross section as shown in the embodiment in FIG. 4, wherein twocavities 4 a and 4 b are provided in the inner part, and wherein thespace between the outermost outer part 5 a and the inner part 6 definesan outer steam passage 3 a and an outer opening 2 a, respectively, andthe space between the inner part 6 and the innermost outer part 5 bdefines an inner steam passage 4 b and an inner opening 2 b,respectively. This embodiment of a steam device is able to coat a verylarge area at a time and thus treat the surface of large products suchas food products, eg. whole cheeses, large vegetables or halvedcarcasses.

[0037] As shown in FIG. 6, it is also possible to form a steam device ofthis type as an open curve. In this embodiment the functional partscorrespond to those shown in FIG. 4 and further details appear from thisportion of the description for which reason reference is made thereto. Asteam device shaped as an open curve is applicable where germs are to beeliminated from the surfaces of unusually shaped products. A system isenvisaged, in which a plurality of steam devices shaped as differentopen curves are arranged in a disinfection apparatus according to theinvention and used in a wide range of different applications.

[0038] In general the disinfection apparatus maybe used in connectionwith steam of a liquid, not necessarily aqueous steam. The disinfectionapparatus may for instance be used in connection with alcohol. In thelatter case various additives, optionally gaseous additives, may beadded to the liquid.

[0039] Even though the disinfection apparatus according to the inventionis described above with reference to the disinfection of the surface offood products, the invention is not restricted to this use. Examples ofother possible applications of the invention include disinfection ofsurfaces of issue samples, disinfection of surgical instruments, surfaceactivation of products in connection with chemical process technologyand pharmaceutical industry or cleaning of food packagings prior to usethereof.

[0040] The invention may further be used in abattoirs, in foodproduction in general, in operating theatres, in clean rooms, inbiotechnological laboratories and livestock buildings, etc.

[0041] The apparatus is not necessarily stationary, but may also be amobile unit.

1. Method for disinfecting a product by surface treatment thereof, steamof a liquid, preferably aqueous steam, and sound, preferably ultrasound,being discharged to the surface of the product, characterised in thatultrasound is generated without inducing cavitation and at the same timeas steam is diffused and made to oscillate at a frequency in theultrasonic range at such a high acoustic pressure that the migration ofthe individual molecules exceeds the dimensions of the bacteria or germsto be killed.
 2. Method according to claim 1, characterised in that thesimultaneous ultrasonic generation is provided by conveying steamthrough an ultrasound generating device causing the steam to oscillateat a frequency in the ultrasonic range.
 3. Method according to claim 2,characterised in that the ultrasound generating device is formed of ajet stream and a cavity.
 4. Method according to claim 2, characterisedin that the ultrasound generating device is formed of a whistle forgenerating steam and ultrasound.
 5. Method according to one or more ofthe preceding claims, characterised by a relatively short processingtime.
 6. Disinfection apparatus for carrying out the method according toclaim 1 comprising a steam device (1) for combatting germs on thesurface of a solid product, especially of a solid food product, saidsteam device (1) having at least one steam passage (3) and an opening(2), characterised in that a cavity (4) is provided adjacent the opening(2) and in use adapted to be supplied with a jet of aqueous steam undera comparatively high pressure through the steam passage (3), whereby theaqueous steam discharged from the opening (2) is made to oscillate at afrequency, preferably an ultrasonic frequency, determined by the cavity(4) and in that the steam device (1) comprises an outer part (5), whoseinner wall defines the outer wall of the steam passage, and an innerpart (6) substantially defining the outer wall of the steam passage (3)and also defining the opening (2), the cavity (4) being providedadjacent said opening.
 7. Disinfection apparatus according to claim 6,characterised in that the cavity (4) is adjustably interspaced from theopening (2) of the steam device.
 8. Disinfection apparatus according toclaim 6, characterised in that the cavity (4) is arranged adjacent theopening (2) and optionally integrally formed therewith.
 9. Disinfectionapparatus according to one of the claims 6-8, characterised in that theouter part (5) and the inner part (6) are thus secured in relation toeach other and that aqueous steam supplied through the steam passage (3)is conveyed towards the cavity (4) substantially in such a manner thatthe aqueous steam is made to oscillate at a frequency, preferably anultrasonic frequency, determined by the cavity.
 10. Disinfectionapparatus according to one of the claims 6-9, characterised in that inconnection with the cavity (4) the steam device (1) is a Hartmanngenerator, a steam jet or a disc jet.
 11. Disinfection apparatusaccording to one of the claims 6-10, characterised in that the steamdevice is shaped as a disc-shaped body.
 12. Disinfection apparatusaccording to one of the claims 6-10, characterised in that the steamdevice is shaped as a rail-shaped body.